Monday, August 24, 2009

Putting OSM On A Diet

I've been fighting to cut an entire set of X-Plane scenery off of OSM...the stickler: Boston. Why Boston happened to be the tile that had this problem I don't know, but basically I ran out of memory. The scenery creation process unfortunately isn't very space efficient and at one point it needs two copies of the roads: a "planar map" for area calculations and a separate "network" version for actual export. I just didn't have enough RAM for two road grids, plus other raw data and a 3-d triangle mesh.

Douglas Peuker to the rescue - a 7m error limit on roads cuts data down by 25% in San Diego and 75% in Boston.

Once I have the whole process working I might raise this limit back up again...the main culprit is small sections of road with very high node counts. In a few cases I found 7m spacing along a road! The data is definitely inconsistent.